Portable, semi-permanent or permanent containment tanks, enclosures or vessels are commonly used in the oil and gas industry, in the mining and mineral processing industries, and for a wide variety of other industries and industrial applications. Such tanks or enclosures are often used to store liquids, slurries or other fluids until such time as they can be further processed or otherwise disposed of or collected and shipped to other locations. An example of a temporary containment vessel is one used in association with oil and gas drilling. When drilling an oil or gas well, drilling mud is typically pumped down the well in order to serve as the source of energy to turn the drill bit. Drilling mud typically contains toxic and/or expensive additives that cannot be released into the environment, or that for economic reasons need to be recovered. In such instances as the mud leaves the casing it is directed to a tank or containment vessel, after which it can be recycled back into the drilling circuit or gathered and shipped for processing, disposal or reuse. A further example of the use of such tanks in the oil and gas industry is to contain large volumes of fluids during fracking operations.
Since in many instances containment tanks or vessels are required on a temporary or semi-permanent basis, they are often formed in a manner that allows them to be transported to the desired location, assembled, used for the desired purpose, disassembled, and then shipped for subsequent use in a different location. To assist in quick assembly and disassembly, the tanks may be formed from a series of individual panels that create the tank's bottom and walls. After the panels have been erected, a liner is typically inserted in order to provide a fluid-tight containment.
In order to drain the contents of the tank, a suction line from a pump can be lowered over one of the tank walls. However, in cold weather applications where the top of the tank is covered in order to prevent freezing of the fluids, deployment of a suction line over a tank wall becomes somewhat more difficult. Further, the pumping equipment used to drain large tanks can be of considerable size and weight, making it sometimes necessary to utilize cranes or other lifting apparatuses in order to lower the suction line into the tank. For that reason, others have proposed installing a drain port within the side wall of the tank. Such ports require the use of a series of bolts, that extend through the tank wall and that secure the drain port within the wall to permit the tank to be drained when desired, while at the same time allowing the drain to be sealed to prevent unintentional leakage of the tank contents. Unfortunately, in the case of large tanks that are lined with a flexible liner, it has been found that the pumping of material into and out of the tank often causes small shifts in the liner. In such cases shifting of the liner puts considerable stress upon the liner material at the locations where the bolts that extend through the tank wall to maintain the drain in place pass through the liner material. The stress upon a liner can cause tearing and shifting of the liner, which in some instances can result in a leakage of the tank contents. Further, the assembly of the drain within the tank is laborious as it typically requires an individual both inside and outside the tank in order to assemble the bolts. Where the tank is to be disassembled, removal of the drain will often require an individual to enter the tank, which may present health hazards depending upon the materials that have been stored therein.